Linear motion resistor



Aug. 14, 1956. M. E. BOURNS 2,759,080

LINEAR MOTION RESISTOR Filed Sept. 14, 1953 IT; 4 I

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flL-WT United States Patent LINEAR MOTION RESISTOR Marian E. Bourns, Riverside, Calif. Application September 14, 1953, Serial No. 379,821

2 Claims. (Cl. 201-62) The present invention relates to variable resistors or potentiometers, and more particularly to that type of instrument wherein a contact-carrying member is moved along the length of a resistance element in a rectilinear manner.

The primary object of the present invention is to provide a new and unique form of resistor construction whereby an instrument of any desired length may be made up from standard components. This object is accomplished by using a three-piece body construction comprising a center section of uniform cross section and end sections attached to opposite ends thereof. The center section is cut to length from a piece of stock of uniform cross section and indeterminate length, and is thereafter assembled with standardized end sections, electrical elements, and a cover to provide a finished instrument of any desired length. The center and end sections of the body are preferably, although not necessarily, formed of nonconductive plastic material which may be molded, extruded, or otherwise shaped to the desired configuration. This arrangement eliminates the necessity for forming a multitude of body sections of various lengths, and greatly simplifies the manufacturing process, as well as minimizing inventory problems.

Another object of the invention is to provide a new and unique form of contact-carrying member which may be extruded or otherwise molded of non-conductive plastic in continuous lengths of bar stock and cut to length; the said member being formed with bearing portions that receive the guiding means of the instrument. In the preferred form illustrated herein, the bearing portions take the form of grooves or channels in opposite sides of the member.

Another important object of the invention is to provide a resistor embodying a molded plastic body, wherein connector plug elements, such as pins or sockets, are molded integrally with the body and are connected to electrical elements mounted on the body. This arrangement permits the instrument to be plugged directly into a companionate connector in the circuit with which it is associated, and eliminates the necessity for soldering or otherwise attaching lead wires to terminals and the like.

A further object of the invention is to provide a new and improved resistor which is simple and inexpensive to manufacture, and wherein the electrical parts are accurately aligned with respect to one another.

The foregoing and other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment thereof, reference being had to the accompanying drawings, wherein:

Figure 1 is a sectional view taken along the longitudinal axis of a resistor embodying the principles of this invention;

Figure 2 is a transverse section of the same, taken at 2-2 in Figure 1; and

Figure 3 is a perspective view of the center body section removed from the instrument.

In the drawings, the reference numeral 10 designates the instrument in its entirety. The body of the instrument is comprised of a center section 11 and end sections 12 and 13. All three sections are preferably, although not necessarily, formed of non-conductive plastic material such as one of the phenolic reisns, which are thermosetting and dimensionally stable. The end sections 12 and 13 may be molded to shape, while the center section 11 may be molded or extruded in long lengths of bar stock that are subsequently cut to length.

The center section 11 is preferably segmental in cross section, as shown in Figure 2, with a cylindrical surface 14 and a flat, top surface 15. Formed in the fiat surface 15 are two laterally spaced, parallel channels 16 and 17, which receive a conductor strip 20 and resistance element 21, respectively. The conductor 20 and resistance element 21 are mounted side by side, and extend parallel to the longitudinal axis of the center section 11. The conductor 20 is preferably in the form of an inverted U- shaped strip of conductive sheet metal, which is seated in the channel 16 with the two legs extending downwardly. The resistance element 21 may be a wire-wound element, as shown, or it may be formed of composition material. The two end sections 12 and 13 are cylindrical in shape and are assembled on opposite ends of the center section 11 with their outer surfaces flush with the cylindrical surface 14 of the center section.

Two laterally spaced locating projections 22 are formed on each of the end sections 12, 13, in the area abutted against by the center section 11, and these locating projections are received within holes 23 drilled or otherwise formed in the end of the center section 11. The locating projections hold the end sections in fixed relation to the center section, and prevent lateral displacement or turning movement between the parts. Telescopically fitted over the three body sections is a tubular sleeve 24, which is attached to the end sections 12, 13 by self-tapping screws 25. O-rings 26 seated within circumferential grooves 27 in the end sections seal the interior of the instrument against dirt and moisture.

Extending parallel to the conductor 2% and resistance element 21 above the fiat surface 15 of the center section 11 are guide means in the form of two laterally spaced rods 30 and 31, the ends of which are mounted in the end sections 12 and 13. A contact-carrying member of non-conductive plastic is slidably mounted on the guide rods 30, 31, and attached to the underneath side thereof is a substantially U-shaped contact 34. One leg of the contact 34 rides on the conductor 20, while the other leg rides on the resistance element 21, thereby forming a bridge. The contact-carrying member 32 is preferably formed by extruding or molding continuous lengths of bar stock of uniform cross section, and then cutting the said bar stock into short lengths to make the member 32. The bar stock is preferably molded with a cross section similar to the configuration shown in Figure 2, with outwardly facing grooves or channels 33 in opposite sides thereof, which receive the guide rods 34 31 and serve as bearing portions therefor.

The contact member 32 is moved along the guide rods 30, 31 by means of a control wire 35, which is inserted into a hole 36 in the member 32, and secured thereto by a set screw 37. The control wire extends through a hole 40 in the end section 13, and is sealed by means of an O-ring 41, which is seated within a counterbore 42 in the end section 13. A sleeve or bushing 43 is pressed into the counterbore 42 to confine and retain the O-ring.

The other end section 12 has three connector plug elements 46 molded integrally therewith, only two of which are to be seen in Figure 1 of the drawings. The connector plug elements 46 may be either male fittings, such as the pins shown in the drawings, or female fittings such as pin sockets. A cavity 47 is molded into the outer face of the end section 12 to receive the socket member into which the elements 46 are inserted. Two of the elements 46 are connected by wires 50 and 51 to opposite ends of the resistance element 21, while the third element! 46 is connected by a wire 5-2 to the conductor 20.

As shown in Figure 3, the wire 50', extending to the far end of the resistance element 21, passes underneath the conductor 20, and at 50a passes up-over'the top of the body section and down into the bottom channel 33,. where it is connected. to the end of the resistance element.

In the practice of the present invention, the instrument is assembled by first cutting a center section 11 to desired length from a long piece of bar stock of the cross: section shown in Figure 2. Locating holes 23 are then drilled or otherwise formed in the ends of the center section, and a. resistance element 21- and conductor 20 are mounted within the channel 17 and 16, respectively. Standardized end sections 12 and 13 are then placed at the ends of the center section, with the locating projections 22 seated within the holes 23. The lead wires 50, 51, and 52 are connected to the plugs 46. Guide rods 31 are cut to length from round bar stock, and a contact member 32 is likewise cut to length from bar stock. The contact member 32 is slidably mounted on the guide rods, which are secured in the end section 12, 13; and the control wire 35 is connected thereto. A tubular sleeve 24' which has been cut to appropriate length from tubing in stock lengths, is then inserted over the body sections to enclose. the electrical components, and is secured to the. end sections 12, 13 by screws 25. By means of this arrangement,.it is possible to make an instrument of any desired length from a minimum of standard components; the various parts which differ in length being merely cut to length from long sections of bar stock.

While Lhave shown and described in considerable detail what Ibelieve to be the preferred form of my invention, it will be understood that various changes may be made in the. shape and arrangement of the several parts thereof without departing from the broad scope of the appended. claims.

I claim:

1. A variable resistor comprising a body made of an elongated center section of generally uniform cross sec-- tion and a pair of upstanding end sections at opposite endsthereof, at least one of said end sections being d'etachably secured to an end of said center section, said center section having a generally flat mounting surface on the top side thereof, a resistance element secured on said mounting surface between said upstanding end sections, a slidably supported contact member disposed above said mounting surface and wiping on said resistance element, an actuating member projecting through one of said end sections and connected to said contact member, and a cover enclosing said center section and and sections and making a snug fitting contact with the end sections so as to provide a moisture tight and dust proof enclosure for said element and contact member.

2. A variable resistor comprising a body made up of an elongated center section of generally uniform cross section and a pair of upstanding end sections secured to opposite ends thereof, said center section having a generally fiat mounting surface on the top side thereof, a resistance element secured on said mounting surface between said upstanding end sections, a pair of guide rods having their ends fixed in said endsections and extending parallel to said resistance element above said mounting surface, acontact member slidably supported on said guide rods and wiping on said resistance element an actuating member slidably projecting through one of said end sections and connected to said contact member, and a tubular case enclosing said body and engaging said end sections with snug fitting contact providing an enclosure for said element and said contact member which is sealedagainst dust and moisture.

References Cited in the file of this patent UNITED STATES PATENTS 2,242,327 Rubinstein May 20, 1941 2,266,412 Cochrane Dec. 16, 1941 2,339,721 Wilson Jan. 18,1944 2,420,807 Aufiero May 20, 1947 2,625,633 Warsher Jan. 13, 1953 2,646,489 McArron July 21, 1953. 2,706,230 Bourns et al Apr. 12, 1955 FOREIGN PATENTS 27,711 The Netherlands July 16, 1932 160,348 Great Britain Mar. 24, 1921' 229,485 Great Britain Feb. 26, 1925 459,067 Great Britain Jan. I, 1937 532,401 France Nov. 14, 1921 544,280 Great Britain Apr. 7, 1942 

